1. Field of the Invention
This invention relates to a radiation thermometer for measuring the temperature of an object of measurement by infrared ray radiated from the object of measurement.
2. Description of the Related Art
As this type of radiation thermometer, a clinical thermometer for measuring with the method disclosed, for example, in the gazette of unexamined published Japanese Patent Application Laid-open No. Sho 61-117422 is known. The clinical thermometer comprises an infrared ray sensor, a probe for taking in infrared ray from an earhole, and a controller for maintaining a sensor temperature of an infrared sensor at a predetermined temperature, and calculates a temperature from an output of the infrared ray sensor and the sensor temperature of the infrared ray sensor maintained at a predetermined temperature. In addition, in another radiation thermometer similar to this type, it calculates a temperature from a measured sensor temperature of an infrared ray sensor and an output of an infrared sensor by measuring temperature of the infrared sensor (sensor temperature) in stead of maintaining it.
In such a radiation thermometer, a temperature of an object of measurement is calculated in accordance with the following logical expression (equation 1) derived from a rule generally known as the Rule of Stefan-Boltzmann (see, for example, xe2x80x9cinfrared radiation engineering: basics and applicationsxe2x80x9d edited by Infrared Ray Technology Research Institute and published by Ohmsha, Ltd.):
Output of infrared ray sensor E=L(Tx4xe2x88x92Ta4)xe2x80x83xe2x80x83Equation 1
where, Tx is an absolute temperature of an object of measurement (an object of measurement temperature);
Ta is an absolute temperature of an infrared ray sensor (a sensor temperature);
E is an output of an infrared ray sensor (a sensor output); and
L is a coefficient indicating the sensitivity of a measurement system.
In the past, with such a radiation thermometer, a sensor temperature was preserved at a reference temperature Ta0, an object of measurement having a known object of measurement reference temperature T0 was measured, and a measurement value was adjusted in accordance with a logical expression such as equation 1 using a calculated sensor output E0. That is to say, during an adjustment, controlling means incorporated in the radiation thermometer determined a coefficient L that could be measured most precisely in accordance with the equation shown by the straight line 101 of FIG. 8 from the above (T0, Ta0, E0), and retained the coefficient in a readable memory from the controlling means. Then, at the time of measurement, the controlling means incorporated in the radiation thermometer read out the coefficient L from the memory and calculated the temperature of the object of measurement in accordance with equation 1 from a sensor output E and a sensor temperature Ta of the infrared ray sensor.
However, in the conventional art as described above, there is a problem that the logical relationship as in the above logical expression (equation 1) cannot necessarily be met depending upon characteristics of parts such as an infrared ray sensor forming a measurement apparatus. For example, the relationship of the above logical expression (equation 1) is shown by the straight line 101, but in an actual measurement, there emerges a gap between the straight line 101 and, for example, the dotted line 100 of FIG. 8.
Therefore, there is a problem that an occurrence of a measurement error cannot be ultimately avoided even if an absolute precision of a measurement value is aimed to be improved in accordance with the logical expression (equation 1) or the Rule of Stefan-Boltzmann, and that parts such as a sensor with high absolute precision are required for restraining such an error.
The present invention has been devised to solve the above mentioned object and it is an object of the present invention to provide a radiation thermometer capable of precise measurement without depending on an absolute precision of an infrared ray sensor for detecting infrared ray or a temperature sensor for measuring a temperature of the infrared ray sensor.
In order to attain the above object, a radiation thermometer of the present invention has the following configuration. A radiation thermometer of the present invention comprises an infrared ray sensor for detecting infrared ray radiated from an object of measurement as a sensor output, a sensor temperature measuring portion for measuring the temperature of the infrared ray sensor itself as a sensor temperature, a controlling means for calculating the temperature of the object of measurement as an object of measurement temperature based oh the sensor output and the sensor temperature, wherein the controlling means for controlling the temperature measurement retains information for an object of measurement reference temperature as an object of measurement temperature to be a reference, information for a sensor reference temperature as a sensor temperature to be a reference, and information for a sensor reference output as a sensor output to be a reference when infrared ray radiated from the object of measurement having the object of measurement reference temperature is detected by the infrared ray sensor having the sensor reference temperature, and calculates the object of measurement temperature of the object of measurement based on a first difference as a difference between a sensor temperature measured by the sensor temperature measuring portion and a sensor reference temperature calculated from the information for the sensor reference temperature, a second difference as a difference between a sensor output detected by the infrared ray sensor and a sensor reference output calculated from the information for a sensor reference output, and the information for an object of measurement reference temperature.
In this case, the controlling means may retain the variation characteristics of an object of measurement temperature specified by the combination of object of measurement temperatures at a plurality of points measured in advance, a sensor temperature and a sensor output, and calculate the object of measurement temperature based on the variation amount of the object of measurement temperature by the first difference, the variation amount of the object of measurement temperature by the second difference, and the information for an object of measurement reference temperature.
In addition, the controlling means may further retain sensor temperature dependent amount calculation information found based on the relationship between each sensor output at the time when the infrared ray sensor detects infrared ray from an object of measurement having a specific object of measurement temperature at different sensor temperatures at a plurality of points, respectively, and each sensor temperature at that time and sensor output dependent amount calculation information found based on the relationship between each sensor output at the time when the infrared ray sensor detects infrared ray from an object of measurement having different object of measurement temperatures of a plurality of points at a specific sensor temperature, respectively, and each object of measurement temperature at that time, and calculate the temperature of the object of measurement based on a relative sensor temperature dependent amount to be calculated based on the first difference and the sensor temperature dependent amount calculation information, a relative sensor output dependent amount calculated based on the second difference and the sensor output dependent amount calculation information, and information for the object of measurement reference temperature.
For this purpose, a sensor reference output at the time when an object of measurement to be a reference having an object of measurement reference temperature is measured by an infrared ray sensor placed under a sensor reference temperature is calculated first in advance. Then, when an object of measurement with an unknown object of measurement temperature is measured at a specific sensor temperature and a specific sensor output is found, the object of measurement temperature of the object of measurement is calculated based on each difference of the sensor temperature and the sensor output from the sensor reference temperature and the sensor reference output.
In this case, a variation amount for the sensor temperature, i.e., a relative sensor temperature dependent amount, may be calculated based on the difference of the sensor temperature from the sensor reference temperature, and a measurement temperature attributable to the sensor output may be calculated in accordance with the logical expression (equation 1).
In addition, a variation amount for the sensor output, i.e., a relative sensor output dependent amount, may be calculated based on the difference of the sensor output from the sensor reference output, and a measurement temperature attributable to the sensor temperature may be calculated in accordance with the logical expression (equation 1).
Further, the temperature measuring means may be equipped with a thermistor or a diode. Further, the infrared ray detecting means may be equipped with a thermopile or a pyroelectric sensor.
Moreover, the variation characteristics may be composed of a biquadratic or less polynominal of one or both of a sensor temperature value and a sensor output value, and the sensor temperature dependent amount calculation information may be represented by a coefficient composing a biquadratic or less polynominal of a sensor temperature value and the sensor output dependent amount calculation information may be represented by a coefficient composing a biquadratic or less polynominal of a sensor output value.